U.S. patent application number 14/982586 was filed with the patent office on 2016-07-07 for developing device and image forming apparatus incorporating same.
The applicant listed for this patent is Naohiro KAWASHIMA, Teppei KIKUCHI, Shinnosuke KOSHIZUKA, Tatsuya KUBO, Atsushi NAKAMOTO, Kazunori SUZUKI, Koichi YAMAZAKI. Invention is credited to Naohiro KAWASHIMA, Teppei KIKUCHI, Shinnosuke KOSHIZUKA, Tatsuya KUBO, Atsushi NAKAMOTO, Kazunori SUZUKI, Koichi YAMAZAKI.
Application Number | 20160195846 14/982586 |
Document ID | / |
Family ID | 56286467 |
Filed Date | 2016-07-07 |
United States Patent
Application |
20160195846 |
Kind Code |
A1 |
KOSHIZUKA; Shinnosuke ; et
al. |
July 7, 2016 |
DEVELOPING DEVICE AND IMAGE FORMING APPARATUS INCORPORATING
SAME
Abstract
A developing device includes a developer bearer, a casing
including a bearing support and a developer container, a developer
conveyor to transport, by rotation, developer in the developer
container, a bearing to fit in the bearing support and support a
shaft of the developer conveyor rotatably on the casing, and a heat
conductor made of a material higher in thermal conductivity than
the bearing support and including a heat absorbing portion to
contact the bearing and absorb heat from the bearing and a heat
dissipating portion to release the heat. The bearing includes an
outer ring secured to the bearing support, an inner ring to rotate
together with the shaft of the developer conveyor, and a ball
disposed between the outer ring and the inner ring. The heat
conductor is disposed to contact the outer ring of the bearing and
contactless with the inner ring and the ball.
Inventors: |
KOSHIZUKA; Shinnosuke;
(Kanagawa, JP) ; YAMAZAKI; Koichi; (Kanagawa,
JP) ; KUBO; Tatsuya; (Kanagawa, JP) ;
NAKAMOTO; Atsushi; (Kanagawa, JP) ; KIKUCHI;
Teppei; (Kanagawa, JP) ; SUZUKI; Kazunori;
(Kanagawa, JP) ; KAWASHIMA; Naohiro; (Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOSHIZUKA; Shinnosuke
YAMAZAKI; Koichi
KUBO; Tatsuya
NAKAMOTO; Atsushi
KIKUCHI; Teppei
SUZUKI; Kazunori
KAWASHIMA; Naohiro |
Kanagawa
Kanagawa
Kanagawa
Kanagawa
Kanagawa
Kanagawa
Kanagawa |
|
JP
JP
JP
JP
JP
JP
JP |
|
|
Family ID: |
56286467 |
Appl. No.: |
14/982586 |
Filed: |
December 29, 2015 |
Current U.S.
Class: |
399/94 |
Current CPC
Class: |
G03G 21/1647 20130101;
G03G 15/0889 20130101; G03G 21/20 20130101 |
International
Class: |
G03G 21/20 20060101
G03G021/20; G03G 15/08 20060101 G03G015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2015 |
JP |
2015-000427 |
Claims
1. A developing device comprising: a developer bearer to bear
developer; a casing including a bearing support and a developer
container to contain the developer; a developer conveyor to
transport, by rotation, the developer in the developer container,
the developer conveyor including a shaft; a bearing to fit in the
bearing support of the casing and support the shaft of the
developer conveyor rotatably on the casing, the bearing including
an outer ring secured to the bearing support, an inner ring to
rotate together with the shaft of the developer conveyor, and a
ball disposed between the outer ring and the inner ring; and a heat
conductor made of a material higher in thermal conductivity than
the bearing support and disposed to contact the outer ring of the
bearing and contactless with the inner ring and the ball, the heat
conductor including a heat absorbing portion to contact the bearing
and absorb heat from the bearing, and a heat dissipating portion to
release the heat absorbed by the heat absorbing portion.
2. The developing device according to claim 1, wherein the shaft of
the developer conveyor and the bearing are made of metal.
3. The developing device according to claim 1, further comprising a
seal to contact the shaft of the developer conveyor at a position
inner than the bearing in an axial direction of the developer
conveyor, wherein the seal seals a developer passage oriented to
the bearing from inside the developer container.
4. The developing device according to claim 1, wherein the heat
conductor comprises an elastic body disposed to contact the outer
ring and made of the material higher in thermal conductivity than
the bearing support.
5. The developing device according to claim 1, wherein the heat
conductor is in tight contact with the outer ring.
6. The developing device according to claim 5, further comprising a
pressing member to secure the heat conductor to the casing and
press the heat conductor against the outer ring.
7. The developing device according to claim 1, wherein the heat
conductor comprises an exposed portion exposed outside the
developing device, and the exposed portion includes a
projection.
8. The developing device according to claim 1, further comprising a
metal part including a projection, wherein the heat conductor
includes an exposed portion exposed outside the developing device,
and the metal part is disposed on the exposed portion.
9. The developing device according to claim 1, wherein the heat
conductor comprises an exposed portion exposed outside the
developing device, and the exposed portion serves as a wall face of
a cooling channel through which cooling air flows to cool the heat
conductor.
10. The developing device according to claim 1, wherein the heat
conductor comprises an exposed portion exposed outside the
developing device, and the exposed portion serves as a wall face of
a cooling channel through which cooling liquid flows to cool the
heat conductor.
11. An image forming apparatus comprising: a latent image bearer to
bear a latent image; and the developing device according to claim 1
to develop the latent image on the latent image bearer with the
developer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is based on and claims priority
pursuant to 35 U.S.C. .sctn.119(a) to Japanese Patent Application
No. 2015-000427, filed on Jan. 5, 2015, in the Japan Patent Office,
the entire disclosure of which is hereby incorporated by reference
herein.
BACKGROUND
[0002] 1. Technical Field
[0003] Embodiments of the present invention generally relate to a
developing device and an image forming apparatus, such as a copier,
a printer, a facsimile machine, or a multifunction peripheral
having at least two of copying, printing, facsimile transmission,
plotting, and scanning capabilities, that include the developing
device.
[0004] 2. Description of the Related Art
[0005] There are developing devices that include a developer
conveyor to transport developer by rotation and a bearing to
rotatably support a rotation shaft of the developer conveyor. In
such developing devices, the bearing is heated with friction.
SUMMARY
[0006] An embodiment of the present invention provides a developing
device that includes a developer bearer to bear developer, a casing
including a bearing support and a developer container to contain
the developer; a developer conveyor including a shaft, a bearing to
fit in the bearing support of the casing, and a heat conductor
including a material higher in thermal conductivity than the
bearing support. The developer conveyor is configured to transport,
by rotation, the developer in the developer container; and the
bearing supports the shaft of the developer conveyor rotatably on
the casing. The bearing includes an outer ring secured to the
bearing support, an inner ring that rotates together with the shaft
of the developer conveyor, and a ball disposed between the outer
ring and the inner ring. The heat conductor is disposed to contact
the outer ring of the bearing and contactless with the inner ring
and the ball. The heat conductor includes a heat absorbing portion
to contact the bearing and absorb heat from the bearing, and a heat
dissipating portion to release the heat absorbed by the heat
absorbing portion.
[0007] In another embodiment, an image forming apparatus includes a
latent image bearer to bear a latent image, and the above-described
developing device to develop the latent image on the latent image
bearer with developer.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0008] A more complete appreciation of the disclosure and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0009] FIG. 1 is an enlarged cross-sectional view of an area around
a bearing, in which an agitation screw fits, disposed on a back
plate of a developing device according to an embodiment;
[0010] FIG. 2 is a schematic diagram illustrating an image forming
apparatus according to an embodiment;
[0011] FIG. 3 is a perspective view, as viewed from a back side, of
a process cartridge according to an embodiment;
[0012] FIG. 4 is a perspective view, as viewed from a front side,
of the process cartridge illustrated in FIG. 3;
[0013] FIG. 5 is a schematic cross-sectional view illustrating the
process cartridge;
[0014] FIG. 6 is an enlarged cross-sectional view of the developing
device illustrated in FIG. 1;
[0015] FIG. 7 is a perspective view of the developing device
illustrated in FIG. 6;
[0016] FIG. 8 is a perspective view of a front plate of the
developing device illustrated in FIG. 7, as viewed from the front
side;
[0017] FIG. 9 is a perspective view of the back plate of the
developing device illustrated in FIG. 7, as viewed from a center
side of the developing device;
[0018] FIG. 10 is a perspective view of a center casing of the
developing device illustrated in FIG. 7, as viewed from the back
side;
[0019] FIG. 11 is a schematic top view of a printer body of the
image forming apparatus illustrated in FIG. 2;
[0020] FIG. 12 is a perspective view of a back end portion of the
developing device illustrated in FIG. 7, from which a gear cover is
removed;
[0021] FIG. 13 is a perspective view of the back end portion of the
developing device illustrated in FIG. 12, from which a gear is
removed;
[0022] FIG. 14A illustrates a heat dissipater having a projection
according to an embodiment;
[0023] FIG. 14B illustrates a heat dissipater having a projection
according to a variation; and
[0024] FIG. 14C illustrates a metal part having a projection
according to another variation.
DETAILED DESCRIPTION
[0025] In describing preferred embodiments illustrated in the
drawings, specific terminology is employed for the sake of clarity.
However, the disclosure of this patent specification is not
intended to be limited to the specific terminology so selected, and
it is to be understood that each specific element includes all
technical equivalents that operate in a similar manner and achieve
a similar result.
[0026] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views thereof, and particularly to FIG. 1, a multicolor
image forming apparatus according to an embodiment of the present
invention is described.
[0027] A tandem-type multicolor laser printer including multiple
photoconductors arranged side by side is described below as an
image forming apparatus according to an embodiment of the present
invention.
[0028] FIG. 2 is a schematic diagram illustrating an image forming
apparatus 500 according to the present embodiment.
[0029] The image forming apparatus 500 can be, for example, a
copier, and includes a printer body 100, a sheet feeder 200 on
which the printer body 100 is mounted, and a scanner 300 fixed
above the printer body 100. The image forming apparatus 500 further
includes an automatic document feeder (ADF) 400 attached on the
scanner 300.
[0030] The printer body 100 includes a tandem unit 20 including
four process cartridges 18Y, 18M, 18C, and 18K (also collectively
"process cartridges 18") for forming yellow (Y), magenta (M), cyan
(M), and black (K) images. It is to be noted that suffixes Y, M, C,
and K attached to each reference numeral indicate that components
indicated thereby are used for forming yellow, magenta, cyan, and
black images, respectively.
[0031] The image forming apparatus 500 further includes an optical
writing unit 21, an intermediate transfer unit 17, a secondary
transfer device 22, a registration roller pair 49, and a belt-type
fixing device 25.
[0032] The optical writing unit 21 includes a light source, a
polygon mirror, an f-.theta. lens, and reflection mirrors, and is
configured to direct laser beams onto surfaces of four
photoconductors 1 according to image data.
[0033] FIG. 3 is a perspective view of one of the four process
cartridges 18 as viewed from the back side of the paper on which
FIG. 2 is drawn. FIG. 4 is a perspective view of the process
cartridge 18 as viewed from the front side of the paper on which
FIG. 2 is drawn. FIG. 5 is a schematic view of the process
cartridge 18. Hereinafter the term "axial direction" means the
direction perpendicular to the surface of the paper on which FIG. 2
or 5 is drawn. The terms "front side in the axial direction" and
"back side in the axial direction" respectively mean those of the
paper on which FIG. 2 or 5 is drawn.
[0034] Since the process cartridges 18Y, 18M, 18C, and 18K are
similar in configuration, the subscripts Y, C, M, and K for color
discrimination are omitted in the description below regarding the
configuration and operation of the process cartridges 18 when color
discrimination is not necessary.
[0035] Each of the process cartridges 18 is inserted into the body
of the image forming apparatus 500, from the front side to the back
side in the axial direction as indicated by arrow A in FIGS. 3 and
4, and mounted therein.
[0036] As illustrated in FIG. 5, the process cartridge 18 includes,
in addition to the drum-shaped photoconductors 1, a drum cleaning
device 72 (72Y, 72M, 72C, or 72K), a charging device 71 (71Y, 71M,
71C, or 71K), and a developing device 4 (4Y, 4M, 4C, or 4K)
disposed around the photoconductor 1. The developing device 4 is an
integral part of the process cartridge 18 and removably installed
in the body of the image forming apparatus 500 together with other
components of the process cartridge 18. The developing device 4
includes a cooling section 120 disposed on a side face of a center
casing 4a made of metal, for example. Additionally, as illustrated
in FIG. 3, a gear cover 401 covers a back end of the developing
device 4 in the axial direction to inhibit adhesion of foreign
substances such as dust to drive transmission gears.
[0037] The drum cleaning device 72 mainly includes a cleaning blade
72a, which is elastic and long in the axial direction, and a
discharge screw 72b. In the drum cleaning device 72, a long side
(contact side or an edge portion) of the cleaning blade 72a is
pressed against the surface of the photoconductor 1 to remove
substances, such as residual toner, from the surface of the
photoconductor 1. The discharge screw 72b discharges the removed
toner outside the drum cleaning device 72. The drum cleaning device
72 further includes a charge remover 72c to which direct voltage is
applied.
[0038] The charging device 71 includes a charging roller 71a
disposed to abut the photoconductor 1 and a charging roller cleaner
71b that rotates while abutting the charging roller 71a.
[0039] The developing device 4 includes the developing roller 5
serving as a developer bearer to supply toner to an electrostatic
latent image on the photoconductor 1 while rotating in the
direction indicated by arrow I in FIG. 5. The center casing 4a of
the developing device 4 defines a developer container (including a
collecting compartment 7, a supply compartment 9, and an agitation
compartment 10) to contain developer. Although two-component
developer including toner and carrier is used in the present
embodiment, one-component development may be employed as long as
the developing device includes a developer conveyor that transports
the developer by rotation.
[0040] The developing roller 5 includes a cylindrical developing
sleeve 5a made of a nonmagnetic material and a magnet roller 5b
disposed inside the developing sleeve 5a. The developing sleeve 5a
rotates around the magnet roller 5b, and the magnet roller 5b
includes multiple stationary magnets. As the developing sleeve 5a
rotates around the magnet roller 5b that generates multiple
magnetic poles, developer moves in the circumferential direction
(in the direction of arc) of the developing roller 5.
[0041] With a developing bias applied from a power source 150 to
the developing sleeve 5a, a developing electrical field is
generated between the developing sleeve 5a and the photoconductor 1
in the developing range. With the development field, the toner in
developer carried on the surface of the developing sleeve 5a is
supplied to the latent image on the surface of the photoconductor
1, developing it.
[0042] The developing device 4 includes a developer doctor 12,
serving as a developer regulator, to adjust to a desired or given
thickness the developer supplied to the developing roller 5. The
developer doctor 12 is disposed downstream from a portion where the
developing roller 5 faces a supply screw 8 in the direction in
which the developing roller 5 rotates.
[0043] The center casing 4a includes a first partition 133 and a
second partition 134. The first partition 133 and the second
partition 134 divide the developer container in the developing
device 4 into the collecting compartment 7, the supply compartment
9, and the agitation compartment 10 (i.e., a stirring
compartment).
[0044] The supply screw 8 is disposed in the supply compartment 9
to transport the developer from the back side to the front side in
the axial direction while supplying the developer to the developing
roller 5. In FIG. 5, the supply screw 8 rotates in the direction
indicated by arrow M.
[0045] The collecting compartment 7 is disposed downstream in the
direction of rotation of the developing roller 5 from the
developing range where the developing roller 5 faces the
photoconductor 1. The developer that has passed through the
developing range falls to the collecting compartment 7 and
collected therein. A collecting screw 6 is disposed in the
collecting compartment 7. The collecting screw 6 transports the
developer in the direction identical to the direction in which the
supply screw 8 transports the developer (hereinafter "developer
conveyance direction"). The supply compartment 9 is on a side of
the developing roller 5, and the collecting compartment 7 is
located below the developing roller 5. The agitation compartment 10
is positioned below the supply compartment 9 and on a side of the
collecting compartment 7. An agitation screw 11 is disposed in the
agitation compartment 10 to transport the developer from the front
side to the back side in the axial direction, while agitating the
developer. The agitation screw 11 rotates in the direction
indicated by arrow C in FIG. 5 and transports the developer in the
direction opposite the developer conveyance direction of the supply
screw 8.
[0046] Each of the collecting screw 6, the supply screw 8, and the
agitation screw 11 serves as a developer conveyor and includes a
shaft and a blade provided on the shaft to transport the developer
axially by rotating.
[0047] The first partition 133 separates, at least partly, the
supply compartment 9 from the agitation compartment 10. The first
partition 133 includes openings 133a (illustrated in FIG. 10)
positioned on the front side and the back side in the axial
direction, and the supply compartment 9 and the agitation
compartment 10 communicate with each other through the openings
133a.
[0048] It is to be noted that the supply compartment 9 and the
collecting compartment 7 are separated by the first partition 133
as well, and the first partition 133 does not include an opening to
allow the supply compartment 9 and the collecting compartment 7 to
communicate with each other.
[0049] The second partition 134 separates the agitation compartment
10 from the collecting compartment 7. The agitation compartment 10
and the collecting compartment 7 communicate with each other in an
area close to a toner supply inlet 95 illustrated in FIG. 7. The
toner supply inlet 95 is positioned on the downstream side in the
developer conveyance direction by the collecting screw 6 and the
upstream side in the developer conveyance direction by the
agitation screw 11.
[0050] The supply compartment 9 includes a developer outlet 94 to
discharge a part of developer contained therein when the level of
the developer in the supply compartment 9 exceeds a predetermined
level. The developer discharged from the developer outlet 94 is
transported through a discharge passage 2 to the outside of the
developing device 4, and a discharge screw 2a is disposed in the
discharge passage 2. The discharge passage 2 is positioned on the
side of the supply compartment 9 via a partition 135. The developer
outlet 94 is an opening in the partition 135 to allow the supply
compartment 9 and the discharge passage 2 to communicate with each
other.
[0051] The charging device 71 uniformly charges the surface of the
photoconductor 1. Then, the optical writing unit 21 directs the
laser beam, which is modulated and deflected, to the charged
surface of the photoconductor 1. The laser beam (exposure light)
attenuates the electrical potential of the portion of the
photoconductor 1 thus exposed, forming an electrostatic latent
image thereon. Then, the developing device 4 develops the
electrostatic latent image on the photoconductor 1 into a toner
image.
[0052] The toner image is primarily transferred from the
photoconductor 1 onto an intermediate transfer belt 110.
Subsequently, the cleaning blade 72a of the drum cleaning device 72
removes toner remaining on the surface of the photoconductor 1.
Further, the charge remover 72c removes electrical potential
remaining on the photoconductor 1, after which the charging device
71 uniformly charges the surface of the photoconductor 1. Thus, the
photoconductor 1 is initialized.
[0053] Next, the intermediate transfer unit 17 is described below
with reference to FIG. 2.
[0054] The intermediate transfer unit 17 includes the intermediate
transfer belt 110, a belt cleaning device 90, a tension roller 14,
a driving roller 15, a secondary-transfer backup roller 16, and
four primary-transfer bias rollers 62 (62Y, 62M, 62C, and 62K).
[0055] The intermediate transfer belt 110 is entrained taut around
multiple rollers including the tension roller 14 and rotates
clockwise in FIG. 2 as the driving roller 15 rotates, driven by a
belt driving motor.
[0056] Each of the four primary-transfer bias rollers 62 is
disposed in contact with an inner circumferential surface of the
intermediate transfer belt 110 and receives a primary transfer bias
from a power supply. The four primary-transfer bias rollers 62
press the intermediate transfer belt 110 against the respective
photoconductors 1 from the inner circumferential side. That is, the
intermediate transfer belt 110 is nipped therebetween, and the nips
are called primary transfer nips. The primary transfer bias causes
a primary-transfer electrical field between the photoconductor 1
and the primary-transfer bias roller 62 in the primary transfer
nip.
[0057] A yellow toner image is transferred from the photoconductor
1Y onto the intermediate transfer belt 110 with the effects of the
primary-transfer electrical field and the nip pressure.
Subsequently, magenta, cyan, and black toner images are transferred
from the photoconductors 1M, 1C, and 1K and superimposed one on
another on the yellow toner image. Thus, a superimposed four-color
toner image is formed on the intermediate transfer belt 110.
[0058] The four-color toner image on the intermediate transfer belt
110 is transferred onto a transfer sheet (i.e., a recording medium)
in a secondary transfer nip (secondary transfer process). The belt
cleaning device 90 is disposed downstream from the secondary
transfer nip in the transfer sheet conveyance direction, nipping
the intermediate transfer belt 110 with the driving roller 15 on
the left in FIG. 2. The belt cleaning device 90 removes toner
remaining on the intermediate transfer belt 110 after the secondary
transfer process.
[0059] The secondary transfer device 22 is described in further
detail below.
[0060] The secondary transfer device 22 is disposed below the
intermediate transfer unit 17 in FIG. 2 and includes a conveyor
belt 24 looped around two tension rollers 23. The conveyor belt 24
rotates counterclockwise in FIG. 2 as at least one of the two
tension rollers 23 rotates.
[0061] The intermediate transfer belt 110 and the conveyor belt 24
are nipped between the secondary-transfer backup roller 16 and the
tension roller 23 on the right in FIG. 2. Thus, the intermediate
transfer belt 110 is in contact with the conveyor belt 24 of the
secondary transfer device 22, and the contact portion is called the
secondary transfer nip.
[0062] A secondary transfer bias opposite in polarity to the toner
is applied to the tension roller 23 on the right from a power
supply. The secondary transfer bias causes a secondary-transfer
electrical field in the secondary transfer nip to electrically
transfer the four-color toner image on the intermediate transfer
belt 110 from the side of the secondary-transfer backup roller 16
toward the tension roller 23.
[0063] Timed to coincide with the four-color toner image, the
registration roller pair 49 forwards the transfer sheet to the
secondary transfer nip, and the four-color toner image is
secondarily transferred onto the transfer sheet with nip pressure
and effects of the transfer electrical field.
[0064] It is to be noted that, instead of applying the secondary
transfer bias to one of the tension rollers 23, a contactless
charger to charge the transfer sheet may be used.
[0065] The sheet feeder 200 disposed below the printer body 100
includes a paper bank 43 in which multiple sheet feeding trays 44
are arranged vertically. Each sheet feeding tray 44 can contain a
bundle of transfer sheets. Each sheet feeding tray 44 is provided
with a sheet feeding roller 42 pressed against the transfer sheet
on the top in the sheet feeding tray 44. As the sheet feeding
roller 42 rotates, the transfer sheet is conveyed to a sheet
feeding path 46.
[0066] Multiple pairs of conveyance rollers 47 are disposed along
the sheet feeding path 46, and the registration roller pair 49 is
positioned close to an end of the sheet feeding path 46. The
transfer sheet is conveyed toward the registration roller pair 49
and then clamped in the nip between the registration roller pair
49.
[0067] Meanwhile, the four-color toner image on the intermediate
transfer belt 110 enters the secondary transfer nip as the
intermediate transfer belt 110 rotates. The registration roller
pair 49 forwards the transfer sheet clamped therebetween so that
the transfer sheet contacts the four-color image in the secondary
transfer nip. Thus, the four-color toner image is transferred onto
the transfer sheet in the secondary transfer nip, forming a
full-color image on the transfer sheet that is white. As the
conveyor belt 24 rotates, the transfer sheet carrying the
full-color toner image is discharged from the secondary transfer
nip and conveyed to the fixing device 25.
[0068] The fixing device 25 includes a belt unit to rotate a fixing
belt 26 looped around two rollers as well as a pressure roller 27
pressed against one of the two rollers of the belt unit. In the
fixing device 25, the fixing belt 26 and the pressure roller 27
press against each other, forming a fixing nip therebetween, and
the transfer sheet conveyed by the conveyor belt 24 is clamped in
the fixing nip.
[0069] A heat source to heat the fixing belt 26 is disposed inside
one of the two rollers of the belt unit. The heated fixing belt 26
heats the transfer sheet nipped on in the fixing nip, and the
full-color toner image is fixed on the transfer sheet with the heat
and nip pressure (fixing process).
[0070] After the fixing process, discharge rollers 56 discharge the
transfer sheet to a stack tray 57 protruding from a side plate of
the printer body 100 on the left in FIG. 2. Alternatively, the
transfer sheet is conveyed again to the secondary transfer nip for
forming an image on the back side thereof.
[0071] To make copies of a bundle of documents, users place the
bundle of documents, for example, on a document table 30 of the ADF
400.
[0072] If the bundle of documents is bound like a book on one side
(side-stitched documents), the bundle is placed on an exposure
glass 32. Specifically, the user lifts the ADF 400 to expose the
exposure glass 32 of the scanner 300, sets the bundle on the
exposure glass 32, and then lowers the ADF 400 to hold the bundle
with the ADF 400.
[0073] Then, the user presses a copy start switch, and the scanner
300 starts reading image data of the documents. When the documents
are set on the ADF 400, the ADF 400 automatically conveys the
documents to the exposure glass 32 before reading the image
data.
[0074] In reading the image data, first and second carriages 33 and
34 start moving, and the first carriage 33 directs an optical beam
from the light source onto the document.
[0075] Subsequently, the optical beam reflected from a surface of
the document is reflected by the mirror of the second carriage 34,
passes through an image forming lens 35, and then enters the
reading sensor 36. Thus, the reading sensor 36 captures the image
data of the document.
[0076] In parallel to reading of image data, components of the
process cartridges 18, the intermediate transfer unit 17, the
secondary transfer device 22, and the fixing device 25 start
operating.
[0077] According to the image data captured by the reading sensor
36, the optical writing unit 21 is driven, and yellow, magenta,
cyan, and black toner images are formed on the respective
photoconductors 1. The developing devices 4 develop the
electrostatic latent images onto the yellow, magenta, cyan, and
black toner images. These toner images are superimposed on the
intermediate transfer belt 110 and become the four-color toner
image.
[0078] Almost simultaneously with the start of image data reading,
the sheet feeder 200 starts feeding sheets. Specifically, one of
the sheet feeding rollers 42 is selectively rotated, and the
transfer sheets are fed from the corresponding sheet feeding tray
44. The transfer sheets are fed one by one to the sheet feeding
path 46, separated by a separation roller 45, after which the pairs
of conveyance rollers 47 convey the transfer sheet to the secondary
transfer nip.
[0079] Instead of the sheet feeding tray 44, the transfer sheets
may be fed from a side tray 51 (i.e., a bypass tray) projecting
from the side of the printer body 100. In this case, a sheet
feeding roller 50 is rotated to feed the transfer sheets from the
side tray 51, and a separation roller 52 forwards the transfer
sheets one by one to a feed path 53 inside the printer body
100.
[0080] When multicolor toner images are formed using two or more
toners, the intermediate transfer belt 110 is disposed with its
upper portion substantially horizontal and in contact with the
photoconductors 1Y, 1M, 1C, and 1K.
[0081] By contrast, when monochrome images (black toner images) are
formed, the upper portion of the intermediate transfer belt 110 is
tilted with the left side of the upper portion in FIG. 2 lowered.
Then, the upper portion of the intermediate transfer belt 110 is
disengaged from the photoconductors 1Y, 1M, and 1C.
[0082] Then, only the photoconductor 1K out of the four
photoconductors 1 is rotated counterclockwise in FIG. 1 to form a
black toner image. At that time, not only the photoconductors 1Y,
1M, and 1C but also the developing devices 4Y, 4M, and 4C are
stopped to prevent wear of the photoconductors 1Y, 1M, and 1C and
waste of developer.
[0083] The developing device 4 is described in further detail
below.
[0084] FIG. 4 is an enlarged cross-sectional view of the developing
device 4 according to the present embodiment, and FIG. 5 is a
perspective view of the developing device 4.
[0085] The developing device 4 includes a front plate 80A and a
back plate 80B respectively attached to the axial ends of the
center casing 4a, which is made of metal and defines the supply
compartment 9, the collecting compartment 7, the agitation
compartment 10, and the cooling section 120. FIG. 8 is a
perspective view of the front plate 80A as viewed from the front
side in the axial direction, and FIG. 9 is a perspective view of
the back plate 80B as viewed from a center side (the front side in
the axial direction). FIG. 10 is a perspective view of the center
casing 4a as viewed from the back side in the axial direction.
[0086] As illustrated in FIG. 10, the center casing 4a made of
metal, such as aluminum, includes the first partition 133, the
second partition 134, and the cooling section 120 formed by
monolithic molding. As illustrated in FIG. 3, the cooling section
120 includes multiple radiating fins each extending in the
longitudinal direction (axial direction). The center casing 4a is
electrically grounded, as illustrated in FIG. 6. Although the
developer container and the cooling section 120 are integral parts
of the center casing 4a being a monolithic molded component,
separate components may be jointed instead.
[0087] As the developer conveyors (the collecting screw 6, the
supply screw 8, and the agitation screw 11) transport the developer
in the developing device 4, the developer is supplied to the
developing roller 5 while circulating inside the developer
container.
[0088] The center casing 4a made of metal is advantageous in
efficiently conducting, to the cooling section 120, the heat
generated by friction between the developer conveyors and the
developer, which arises when the developer conveyors are driven,
and friction among developer particles. The heat can be effectively
released from the developing device 4 with the cooling section 120,
thereby suppressing temperature rise inside the developing device
4. As a result, decreases in the charge amount of toner caused by
the temperature rise in the developing device 4 are suppressed, and
toner is inhibited form being fused and from adhering to the
developer doctor 12 or the developing roller 5. Thus, degradation
of image quality is inhibited.
[0089] FIG. 11 is a schematic top view of the printer body 100 of
the image forming apparatus 500.
[0090] As illustrated in FIG. 11, the printer body 100 includes a
front plate 100a serving as an inner cover and disposed on the
front side in the axial direction, and fans 255Y, 255M, 255C, and
255K (collectively "fans 255") are disposed on the front plate
100a. The fans 255 send air to the cooling sections 120 of the
developing devices 4, respectively. In FIG. 11, arrows W indicate
airflow directions inside the printer body 100, and reference
numeral 40 (40Y, 40M, 40C, and 40K) represent a heat conduction
plate.
[0091] The fan 255K faces a cooling channel RK for black located
between the developing device 4K and the drum cleaning device 72C
for cyan. The fan 255C faces a cooling channel RC for cyan located
between the developing device 4C and the drum cleaning device 72M
magenta. The fan 255M faces a cooling channel RM for magenta
located between the developing device 4M and the drum cleaning
device 72Y yellow. The fan 255Y faces a cooling channel RY for
yellow located between a left wall 254 of the printer body 100 and
the developing device 4Y.
[0092] No units such as the process cartridges 18 for other colors
are disposed facing the side of the developing device 4Y on which
the cooling section 120Y is disposed. Accordingly, in the present
embodiment, the left wall 254 is disposed to face the cooling
section 120Y for yellow to define the cooling channel RY between
the left wall 254 and the cooling section 120.
[0093] An exhaust duct 250 is disposed on the back side (back side
in the axial direction) of the printer body 100. The exhaust duct
250 includes duct entrances 251Y, 251M, 251C, and 251K
(collectively "duct entrances 251") to communicate with the cooling
channel RY, RM, RC, and RK (collectively "cooling-air channels R"),
respectively. The exhaust duct 250 connects to an exhaust fan 252
disposed facing a vent of the printer body 100.
[0094] As the developing device 4 is mounted in the image forming
apparatus 500 and the image forming apparatus 500 is driven, the
four fans 255 and the exhaust fan 252 are driven, and air flows
through the cooling-air channels R. The air cools the cooling
sections 120, after which the air is exhausted from the apparatus
by the exhaust fan 252.
[0095] The center casing 4a is made of a conductive metal and
grounded electrically, which attains the following effects.
[0096] If the center casing 4a is made of an insulative material
such as plastic, it is possible that electrical charges of charged
developer charge up the center casing 4a, resulting in image
failure. For example, the charged center casing 4a attracts the
toner circulating therein and causes the toner to adhere to a wall
face thereof. When the toner falls from the center casing 4a and is
used in image developing, spots appear in images, or toner is
partly absent in images like white dots. Additionally, in a
configuration in which the intermediate transfer belt 110 is
situated below the developing device 4, it is possible electrical
force acts between the charged center casing 4a and the toner image
on the intermediate transfer belt 110. Such electrical force can
disturb the toner image, resulting in scattering of toner or fading
of the image.
[0097] In the developing device 4 according to the present
embodiment, electrically grounding the conductive center casing 4a
can prevent the above-described failures induced by the charging up
of the center casing 4a.
[0098] Additionally, the center casing 4a is an extruded metal
product. Use of an extruded product is advantageous in producing
the center casing 4a that is relatively long and includes a tubular
portion with its cross-sectional shape uniform in the longitudinal
direction.
[0099] As illustrated in FIG. 10, the second partition 134 of the
center casing 4a includes an opening 134a positioned on the back
side in the axial direction. The opening 134a allows the agitation
compartment 10 and the collecting compartment 7 to communicate with
each other. The opening 134a in the second partition 134 penetrates
a bottom side of the center casing 4a. To the opening 134a, a toner
concentration sensor is mounted to detect the concentration or
density of toner close to the downstream end in the direction in
which the developer is transported in the agitation compartment 10.
When the developing device 4 is used, the opening 134a is closed
with the toner concentration sensor and fitting parts thereof.
[0100] The front plate 80A illustrated in FIG. 8 and the back plate
80B illustrated in FIG. 9 have capabilities to rotatably support
the developing roller 5, the collecting screw 6, the supply screw
8, and the agitation screw 11 via bearings. The front plate 80A and
the back plate 80B are molded with resin and include hollow
portions in which the bearings are fitted.
[0101] An inner face enclosing the hollow defines bearing insertion
portions (i.e., bearing engagement portions) 81, 82, 83, and
84.
[0102] Into the bearing insertion portions 81 (81A and 81B), the
bearings of the developing roller 5 are fitted. Into the bearing
insertion portions 82 (82A and 82B), the bearings of the collecting
screw 6 are fitted. Into the bearing insertion portions 83 (83A and
83B), the bearings of the supply screw 8 are fitted. Into the
bearing insertion portions 84 (84A and 84B), agitation bearings 76
of the agitation screw 11 are fitted. The bearings are fitted in
the respective bearing insertion portions 81, 82, 83, and 84 by
press fit and secured to the front plate 80A and the back plate
80B. Then, the positions of the developing roller 5, the collecting
screw 6, the supply screw 8, and the agitation screw 11 are
determined relatively to the front plate 80A and the back plate
80B. Simultaneously, the relative positions of the developing
roller 5, the collecting screw 6, the supply screw 8, and the
agitation screw 11 are determined.
[0103] The front plate 80A and the back plate 80B include the
multiple bearing insertion portions and thus are complicated in
shape. It is difficult to produce a complicated shape with a high
degree of accuracy by shaving metal or casting. In the developing
device 4 according to the present embodiment, the front plate 80A
and the back plate 80B are made of resin material.
[0104] The front plate 80A and the back plate 80B are screwed to
both ends of the center casing 4a in the axial direction.
[0105] FIG. 12 is a perspective view of the back end portion of the
developing device 4 in the axial direction, from which the gear
cover 401 is removed. FIG. 13 is a perspective view of the back end
portion of the developing device 4 in the axial direction, from
which gears are removed from the state illustrated in FIG. 12.
[0106] As illustrated in FIG. 12, multiple gears are disposed
inside the gear cover 401. A supply driving gear 802 is secured to
a supply screw shaft 801 of the supply screw 8. A collecting
driving gear 602 is secured to a collecting screw shaft 601 of the
collecting screw 6. An agitation driving gear 112 is secured to an
agitation screw shaft 111 of the agitation screw 11.
[0107] A first stud 301 and a second stud 303 are disposed on the
back plate 80B, and a first idler gear 302 and a second idler gear
304 rotatably mesh with the first stud 301 and the second stud
303.
[0108] As illustrated in FIGS. 12 and 13, the supply driving gear
802, the collecting driving gear 602, and the agitation driving
gear 112 are secured to the axial ends of the supply screw shaft
801, the collecting screw shaft 601, and the agitation screw shaft
111. Each of the supply driving gear 802, the collecting driving
gear 602, and the agitation driving gear 112 includes a detent
(i.e., a rotation stopper). A drive input gear 803 disposed on the
supply screw shaft 801 serves as a drive transmission member to
transmit driving force input from the body of the image forming
apparatus 500 to the developer conveyors of the developing device
4. The drive input gear 803 transmits the driving force, via the
supply driving gear 802 secured on the supply screw shaft 801, to
the shafts of other developer conveyors.
[0109] Next, specific features of the developing device 4 according
to the present embodiment are described below.
[0110] FIG. 1 is an enlarged cross-sectional view of an area around
the bearing insertion portion 84B of the back plate 80B.
[0111] The developing device 4 includes the agitation screw 11 that
transports the developer in the agitation compartment 10 serving as
the developer container of the developing device 4. The developing
device 4 further includes agitation bearings 76 to support the
agitation screw shaft 111 and rotatably supports the agitation
screw shaft 111 on the back plate 80B (the bearing insertion
portions 84 in particular), which is a bearing support of the
developing casing forming the agitation compartment 10.
[0112] The agitation bearing 76 is a ball bearing and includes a
ball 74 (rolling element) disposed between an outer ring 73 and an
inner ring 75. The outer ring 73 is secured to the back plate 80B,
and the inner ring 75 rotates together with the agitation screw
shaft 111. Regarding the bearing to support a rotator such as the
developer conveyor rotatably on the casing of the developing
device, a rolling bearing is smaller in rotation resistance than a
plain bearing. Accordingly, the rolling bearing is advantageous
over the plain bearing in reducing the driving load of the
developing device.
[0113] The developing device 4 further includes the heat conduction
plate 40 and an elastic heat conduction sheet 41 made of a material
higher in thermal conductivity than the back plate 80B made of
resin. The heat conduction sheet 41 is disposed to contact the
outer ring 73 but not to contact the inner ring 75 and the ball 74.
The heat conduction plate 40 and the heat conduction sheet 41
together serve as a heat conductor. In the present embodiment, the
heat conductor is a thin part, for example.
[0114] The agitation screw shaft 111 is supported via the agitation
bearing 76 by the back plate 80B. The driving force input to the
supply driving gear 802, from the body of the image forming
apparatus 500, is transmitted to the agitation driving gear 112,
and the agitation screw 11 is driven.
[0115] As illustrated in FIG. 1, an agitation seal 77 is attached
to the back plate 80B so that an inner face of the agitation seal
77 contacts the agitation screw shaft 111. The agitation seal 77 is
disposed to contact the agitation screw shaft 111) at a position
inner than the agitation bearing 76 in the axial direction. As the
agitation screw shaft 111 rotates, the agitation seal 77 slidingly
contacts the agitation screw shaft 111. The agitation seal 77 is
elastic and includes an opening positioned at its center and
smaller in diameter than the agitation screw shaft 111. As the
agitation screw shaft 111 penetrates the opening, a periphery of
the opening deforms and tightly contacts the surface of the
agitation screw shaft 111. The agitation seal 77 may be an integral
part of a molded piece including the back plate 80B. Alternatively,
the agitation seal 77 may be a separate part attached to the back
plate 80B with glue or the like.
[0116] If the developer in the agitation compartment 10 enters the
bearing insertion portion 84B on the back side, there are risks
that the developer solidifies between the back plate 80B and the
agitation screw shaft 111 and adheres to the agitation bearing 76
and solidifies thereon, inhibiting the rotation of the agitation
screw 11.
[0117] By contrast, in the present embodiment, the agitation seal
77 tightly contacting the agitation screw shaft 111 inhibits the
developer from entering the bearing insertion portion 84B, thereby
securing the rotation of the agitation screw 11.
[0118] Since the agitation screw shaft 111 rotates with the
agitation seal 77 in tight contact therewith, the agitation seal 77
and the agitation screw shaft 111 are heated by frictional heat.
Unless the heated agitation seal 77 and the agitation screw shaft
111 are cooled, temperature rises in the vicinity of the contact
portion between the agitation seal 77 and the agitation screw shaft
111, and the toner in the adjacent developer melts and coheres
locally. If the toner cohering into aggregation is mixed in the
developer, it is possible that the toner aggregation gets stuck in
the clearance (i.e., a doctor gap) between the developer doctor 12
and the developing roller 5, resulting substandard images including
white lines, where toner is absent. When the toner aggregation
passes the doctor gap and used in image developing, it is possible
that the toner aggregation is transferred from the photoconductor 1
on to the transfer sheet and becomes spots on the image. When the
toner aggregation remains on the photoconductor 1, the image has
void at that position (i.e., white spots).
[0119] The developing device 4 includes the cooling section 120 on
the side face of the metal center casing 4a to cool the developer
in the developing device 4. The agitation seal 77 and the agitation
screw shaft 111, however, are located on the back plate 80B not the
center casing 4a, and the back plate 80B is made of resin lower in
thermal conductivity. Accordingly, heat is not easily conducted
from the agitation seal 77 and the agitation screw shaft 111 to the
cooling section 120. Even if the cooling section 120 is cooled, the
effect to suppress the temperature rise of the agitation seal 77
and the agitation screw shaft 111 is low.
[0120] Referring to FIGS. 1 and 12, the end face of the developing
device 4 on the back side in the axial direction is covered with
the multiple gears made of resin, and the gear cover 401 covers the
multiple gears. This configuration does not allow direct cooling of
the agitation screw shaft 111 and the agitation bearing 76. In this
case, a conceivable approach is to direct air to the agitation
driving gear 112 secured to the agitation screw shaft 111 to cool
the agitation screw shaft 111 via the agitation driving gear 112.
However, the agitation driving gear 112 is made of resin and low in
thermal conductivity. It is difficult to release heat from the
agitation screw shaft 111 and the agitation bearing 76 by directing
air to the agitation driving gear 112.
[0121] In the developing device 4 according to the present
embodiment, the heat conduction plate 40 made of metal and the heat
conduction sheet 41 higher in thermal conductivity than the back
plate 80B are disposed between the back plate 80B and the agitation
driving gear 112. The heat conduction plate 40 contacts the heat
conduction sheet 41, and the heat conduction sheet 41 contacts the
outer ring 73 of the agitation bearing 76.
[0122] The heat conduction plate 40 includes a heat absorber 40a to
and a heat dissipater 40b. For example, the heat conduction plate
40 is made of a sheet metal bent into the heat absorber 40a to face
the outer face of the back plate 80B and the heat dissipater 40b.
The heat absorber 40a extends to the rim of the end face of the
back plate 80B, at which the heat absorber 40a is bent into the
heat dissipater 40b. With this construction, the heat dissipater
40b serves as a wall face defining the cooling channel R as
illustrated in FIGS. 11 and 13.
[0123] The frictional heat generated between the inner ring 75,
which rotates with the agitation screw shaft 111, and the ball 74,
as well as the frictional heat generated between the ball 74 and
the outer ring 73 is conducted to the outer ring 73 and further
conducted to the heat absorber 40a of the heat conduction plate 40
via the heat conduction sheet 41. The frictional heat generated
between the agitation seal 77 and the agitation screw shaft 111 is
conducted from the agitation screw shaft 111 to the inner ring 75
of the agitation bearing 76 and further to the ball 74 and the
outer ring 73. The heat is conducted from the outer ring 73 via the
heat conduction sheet 41 to the heat absorber 40a of the heat
conduction plate 40. The heat is conducted from the heat absorber
40a through the heat conduction plate 40 and released from the heat
dissipater 40b. Thus, the agitation screw 11 is inhibited from
being heated by the frictional heat generated in the agitation
bearing 76 and the frictional heat generated in the contact portion
between the agitation seal 77 and the agitation screw shaft
111.
[0124] Since the heat conduction sheet 41 does not contact the
inner ring 75 and the ball 74, frictional heat is not generated in
the portion where the agitation bearing 76 contacts the heat
conduction sheet 41. This can reduce the number of portions heated
with the friction caused by the rotation of the agitation screw 11,
and the amount of heat generated in the agitation bearing 76 is
reduced. Thus, the temperature rise of the agitation screw 11 is
suppressed, thereby inhibiting adhesion of toner caused by the
heated agitation screw 11 and inhibiting image failure such as
white lines, spots, and white spots.
[0125] As illustrated in FIG. 11, the fan 255 and the exhaust fan
252, which are disposed in the image forming apparatus 500,
generate the airflow in the cooling-air channels R defined along
the cooling section 120 of the developing device 4. The airflow
promotes the heat release from the heat dissipater 40b and further
inhibits the temperature rise of the contact portion between the
agitation seal 77 and the agitation screw shaft 111. Thus, adhesion
of toner is inhibited.
[0126] In FIG. 14A, the heat dissipater 40b includes fins 412
similar to the radiating fins of the cooling section 120. The fins
412 are projections projecting outward from the heat dissipater
40b.
[0127] Providing a projection on the heat dissipater 40b, which
defines a part of the cooling channel R, is advantageous in
increasing the surface area cooled by the airflow in the cooling
channel R and enhancing the cooling effect.
[0128] FIG. 14B illustrates a variation of the projections of the
heat dissipater 40b. In FIG. 14B, the heat dissipater 40b includes
projecting portions 414 instead of the fins 412. Alternatively, the
cooling effect is enhanced similarly by attaching a metal part 416
having projecting portions 414, illustrating in FIG. 14, to the
channel defining face of the heat dissipater 40b.
[0129] Although the present embodiment employs air cooling and air
flows in the cooling channel R, in another embodiment, liquid such
as radiator liquid or coolant flows in the cooling channel R and
similar effects are attained.
[0130] Although the heat conduction plate 40 contacts the outer
ring 73 of the agitation bearing 76 via the heat conduction sheet
41 in the present embodiment, alternatively, the heat conduction
plate 40 may directly contact the outer ring 73. Regarding outer
rings usable for the agitation bearing 76, there are outer rings
having end faces that are not flat. When the end face is not flat,
the area of contact with the heat conduction plate 40 is smaller,
and the heat conduction efficiency is reduced. By contrast, in the
present embodiment in which the heat conduction plate 40 contacts
the outer ring 73 via the heat conduction sheet 41, the heat
conduction sheet 41 deforms conforming to the end face of the outer
ring 73, and the area of contact with the outer ring 73 increases.
Thus, the heat conduction efficiency is increased.
[0131] Additionally, the heat conduction plate 40 is attached to
the outer face of the back plate 80B with a screw 410 (illustrated
in FIG. 13) serving as a pressing member in the present embodiment.
The pressing member to press the heat conduction plate 40 is not
limited to the screw 410 but include a clip, a pin, a spring clamp,
and the like.
[0132] Thus, the heat conduction plate 40 is pressed to tightly
contact the outer ring 73 via the heat conduction sheet 41. With
this construction, clearance is not allowed between the outer ring
73 and the heat conduction sheet 41 as well as between the heat
conduction sheet 41 and the heat conduction plate 40. Thus, the
heat conduction efficiency from the agitation bearing 76 to the
heat conduction plate 40 is enhanced.
[0133] Regarding the ball bearing used in the agitation bearing 76
according to the present embodiment, the outer ring 73, the ball
74, and the inner ring 75 are made of iron, and the agitation screw
shaft 111 of the agitation screw 11 is made of iron as well. Use of
the iron ball bearing for the agitation bearing 76 and the iron
shaft for the agitation screw shaft 111 is advantageous in
increasing the efficiently of heat conduction from the agitation
screw shaft 111, via the agitation bearing 76, to the heat
conduction plate 40. Since the agitation screw shaft 111 that
contacts the agitation seal 77 is made of metal higher in thermal
conductivity, the frictional heat caused between the agitation seal
77 and the agitation screw shaft 111 is efficiently conducted to
the heat conduction plate 40 via the agitation screw shaft 111 and
the agitation bearing 76.
[0134] In the developing device 4 according to the present
embodiment, the agitation screw 11 is higher in rotation speed than
the supply screw 8, and the agitation screw 11 and the collecting
screw 6 are identical in rotation speed. Accordingly, as
illustrated in FIGS. 12 and 13, the heat absorber 40a of the heat
conduction plate 40 extends to a position facing the bearing of the
collecting screw 6 on the back side in the axial direction so that
the heat conduction plate 40 absorbs heat also from the bearing of
the collecting screw 6. Although the heat conduction plate 40 does
not absorb heat from the bearing of the supply screw 8 in the
present embodiment, in another embodiment, a similar structure is
used to cool the bearing of the supply screw 8.
[0135] As illustrated in FIG. 8, the bearing insertion portion 82A
and the bearing insertion portion 84A, to which the front side
bearings of the collecting screw 6 and the agitation screw 11 are
respectively fitted, are disposed at the end of the developing
device 4 on the front side in the axial direction. The end faces of
the bearings fitted to the bearing insertion portions 82A and 84A,
respectively, are exposed, and these bearings can be cooled
directly. Accordingly, heat is less likely to accumulate on these
bearings. Therefore, in the present embodiment, the heat conduction
plate 40 is disposed only on the back side in the axial direction.
However, the developing device 4 may further include a heat
conduction plate to contact the bearings on the bearings of the
front side in the axial direction to promote the release of
heat.
[0136] The various aspects of the present specification can attain
specific effects as follows.
[0137] Aspect A
[0138] A developing device that includes a developer bearer (e.g.,
the developing roller 5); a developer conveyor (e.g., the agitation
screw 11) including a rotation shaft (e.g., the agitation screw
shaft 111) and configured to transport, by rotation, developer in a
developer container (e.g., the agitation compartment 10); a bearing
(e.g., the agitation bearing 76) to fit in a bearing support (e.g.,
the bearing insertion portion 84) of a casing that defines the
developer container (e.g., the center casing 4a, the front plate
80A, and the back plate 80B) and configured to support the rotation
shaft (e.g., the agitation screw shaft 111) rotatably on the
casing; a heat conductor (e.g., the heat conduction plate 40 and
the heat conduction sheet 41) made of a material higher in thermal
conductivity than the bearing support (e.g., the bearing insertion
portion 84 of the back plate 80B) that supports the bearing (e.g.,
the agitation bearing 76). The heat conductor includes a heat
absorbing portion (e.g., the heat absorber 40a and the heat
conduction sheet 41) to contact the bearing and absorb heat from
the bearing, and a heat dissipating portion (e.g., the heat
dissipater 40b) to release the heat absorbed by the heat absorbing
portion. The bearing includes an outer ring (e.g., the outer ring
73) secured to the bearing support, an inner ring (e.g., the inner
ring 75) to rotate together with the rotation shaft, and a ball
(e.g., the ball 74) disposed between the outer ring and the inner
ring. The heat conductor is disposed to contact the outer ring of
the bearing and disengaged from the inner ring and the ball.
[0139] It is to be noted that the developer conveyor including the
rotation shaft is not limited to a screw but can be an auger or a
paddle.
[0140] According to Aspect A, as described above, since the heat
conductor does not contact the inner ring of the bearing, the
number of portions heated by the friction is reduced compared with
a configuration in which the heat conductor contacts the inner
ring, thereby generating frictional heat. With this configuration,
in the configuration using the rolling bearing for the developer
conveyor, the amount of heat generated by the rotation of the
developer conveyor is reduced. Accordingly, the developer conveyor
is inhibited from being heated with the frictional heat, which
arises as the developer conveyor rotates.
[0141] Aspect B
[0142] In Aspect A, the shaft (e.g., the agitation screw shaft 111)
of the developer conveyor and the bearing (e.g., the agitation
bearing 76) are made of metal.
[0143] Aspect B attains a heat conduction structure to efficiently
conduct heat from the rotation shaft via the bearing to the heat
conductor (e.g., the heat conduction plate 40).
[0144] Aspect C
[0145] The developing device according to Aspect A or B further
includes a seal (e.g., the agitation seal 77) to contact the shaft
(e.g., the agitation screw shaft 111) at a position inner than the
bearing (e.g., the agitation bearing 76) in the axial direction to
seal a developer passage (e.g., the agitation compartment 10)
through which the developer moves from inside the developer
container to the bearing.
[0146] This configuration can inhibit the developer from inhibiting
the rotation of the developer conveyor such the agitation screw 11.
Additionally, even when frictional heat is generated in the contact
portion between the seal and the rotation shaft, the heat conductor
(e.g., the heat conduction plate 40 and the heat conduction sheet
41) release the heat via the rotation shaft and the bearing.
Accordingly, the developer conveyor is inhibited from being heated
with the frictional heat, which arises as the developer conveyor
rotates.
[0147] In particular, the rotation shaft and the bearing both made
of metal enhance the thermal conductivity of the components to
provide a route of heat conduction from the contact portion between
the seal and the rotation shaft to the heat conductor. Accordingly,
the frictional heat caused between the seal and the rotation shaft
is released efficiently.
[0148] Aspect D
[0149] In any one of Aspects A through C, the heat conductor (e.g.,
the heat conduction plate 40 and the heat conduction sheet 41)
includes an elastic body (e.g., the heat conduction sheet 41)
disposed in the contact portion with the outer ring, and the
elastic body is made of a material higher in thermal conductivity
than the bearing support such as the back plate 80B.
[0150] As described above, this aspect can increase the area of
contact between the heat conductor and the outer ring, thereby
enhancing the thermal conductivity from the bearing to the heat
conductor.
[0151] Aspect E
[0152] In any one of Aspects A through D, the heat conductor (e.g.,
the heat conduction plate 40 and the heat conduction sheet 41) is
pressed to the outer ring to contact the outer ring.
[0153] Accordingly, the thermal conductivity from the bearing to
the heat conductor is enhanced.
[0154] Aspect F
[0155] In any one of Aspects A through E, the heat conductor (e.g.,
the heat conduction plate 40 and the heat conduction sheet 41)
includes an exposed portion (e.g., the heat dissipater 40b)
disposed outside the developing device, and the exposed portion has
a projection.
[0156] Accordingly, the surface area of the heat dissipating part
of the heat conductor is increased, thereby enhancing the cooling
effect.
[0157] Aspect G
[0158] In any one of Aspects A through E, the heat conductor (e.g.,
the heat conduction plate 40 and the heat conduction sheet 41)
includes an exposed portion (e.g., the heat dissipater 40b)
disposed outside the developing device, and a metal part having a
projection is disposed in the exposed portion.
[0159] This aspect can increase the surface area of the heat
conductor to release heat from the heat conductor to the outside of
the developing device, thereby enhancing the cooling effect.
[0160] Aspect H
[0161] In any one of Aspects A through G, the heat conductor (e.g.,
the heat conduction plate 40 and the heat conduction sheet 41)
includes an exposed portion (e.g., the heat dissipater 40b)
disposed outside the developing device, and the exposed portion
serves as a wall face of a cooling channel (e.g., the cooling
channel R) through which cooling air or cooling gas flows.
[0162] With this aspect, as described in the embodiments, the
airflow promotes the release of heat from the exposed portion of
the heat conductor, thereby enhancing the effect to inhibit the
temperature rise of the developer conveyor such as the agitation
screw 11.
[0163] Aspect I
[0164] In any one of Aspects A through G, the heat conductor (e.g.,
the heat conduction plate 40 and the heat conduction sheet 41)
includes an exposed portion (e.g., the heat dissipater 40b)
disposed outside the developing device, and the exposed portion
serves as a wall face of a cooling channel (e.g., the cooling
channel R) through which cooling liquid such as radiator liquid
flows.
[0165] With this aspect, as described in the embodiments, the flow
of liquid promotes the release of heat from the exposed portion of
the heat conductor, thereby enhancing the effect to inhibit the
temperature rise of the developer conveyor such as the agitation
screw 11.
[0166] Aspect J
[0167] In an image forming apparatus, such as the image forming
apparatus 500, that includes a latent image bearer (e.g., the
photoconductor 1) and a developing device to develop the latent
image on the latent image bearer, the developing device according
to any of aspects A through I is used.
[0168] Accordingly, the image forming apparatus can inhibit the
occurrence of image failure such as white lines, spots, and white
spots as described above.
[0169] Numerous additional modifications and variations are
possible in light of the above teachings. It is therefore to be
understood that, within the scope of the appended claims, the
disclosure of this patent specification may be practiced otherwise
than as specifically described herein.
* * * * *